Wildfire burn scars impacting Western water availability by shifting the way snow melts: Study

As increasingly intense wildfires climb to higher elevations across the U.S. West, the burn scars they leave behind are shifting the way snow is melting, a new study has found.

The accumulation of snowpack, which appears in rivers as runoff in the spring, is an important source of water in the drought-stricken region.

For that reason, the changes to the landscape that are being wrought by wildfires are complicating water availability assessments, according to the study, published in Water Resources Research.

A Colorado-based research team decided to examine such shifts by looking at the aftermath of the 2020 Cameron Peak Fire — the state’s largest fire on record, which burned for nearly four months across federal, state and private lands.

Examining the impacts of the fire on snowpack across various types of mountainous terrain, the scientists determined that location was key to when the snow melted, and how quickly.

Specifically, they found that the amount of water contained in snow tended to peak earlier in the season at burn sites on south-facing slopes, which receive more sun.

This turning point occurred 22 days earlier at south-facing burn locations than at north-facing spots at the same elevation, due to the heightened absorption of solar radiation and the lack of trees available to intercept the sun’s rays, according to the study.

In addition, snow on these south-facing burn scars finished melting entirely 11 days sooner than snow accumulated on the charred north-facing areas, the authors found.

Not only does the south-facing snowpack lose its tree-covered shield, but it also can be darkened by the soot and ash from tree trunks that remain after a wildfire, per the study.

The darkened color, in turn, reduces the snow’s reflectivity and enables it to absorb more solar energy and melt faster, the authors explained.

Four years past the fire, they observed that while the snowpack is noticeably cleaner, the trees have not come back — and may never do so. The unshaded, south-facing slopes that now accumulate less snow may be too dry for tree seedlings to take root, the researchers noted.

“These south-facing slopes may be transformed for good and not recover to their pre-fire state,” co-author Dan McGrath, an associate professor of geosciences at Colorado State University, said in a statement.

Emphasizing that the watershed may be forever changed, the researchers warned of lasting uncertainty for resources downstream. Nonetheless, they stressed the importance of continuing to quantify burn-related field impacts, as doing so could help improve resource management.

“When you consider the amount of area that has burned across the western U.S., which is increasingly occurring at high elevations that accumulate deep snowpacks, this is a really critical issue that has and will continue to impact the region’s water supply,” McGrath said.